Photo/Illutration About 7,800 tons of treated radioactive water will be released into the ocean from the Fukushima No. 1 nuclear power plant between Oct. 5 and 23. (Takeshi Iwashita)

The second round of releasing treated radioactive water from the Fukushima No. 1 nuclear plant began Oct. 5, with the plant operator stressing radiation levels remain far below the safety limit.

Plant engineers turned on the pump at 10:18 a.m., discharging the water with traces of tritium, a radionuclide inseparable from water, into the Pacific Ocean.

After being diluted with seawater, about 7,800 tons of treated water will be released by Oct. 23, according to Tokyo Electric Power Co.

The same amount of water was poured into the sea in August and September in the first round.

TEPCO said tests ahead of the second release showed the tritium concentration of the diluted water was below 1,500 becquerels per liter, which is one-40th the government’s legal standard, as specified in the plan approved by the Nuclear Regulation Authority.

The plant is generating massive amounts of radioactive water each day as TEPCO continues using water to cool melted nuclear fuel in reactors damaged by the Great East Japan Earthquake and tsunami in 2011.

Most radioactive elements in the water can be removed through treatment processes, but tritium will remain.

The treated water also contains a trace amount of other radioactive materials, including cesium.

Ahead of the second discharge, TEPCO, a private research laboratory and the Japan Atomic Energy Agency each measured the concentration of such radioactive materials, 29 of them in all, in the undiluted treated water.

All results from the three organizations showed the concentrations below the legal standards, according to TEPCO.

Following the first round, no significant change was observed regarding tritium concentrations in the seawater sampled around the plant and fish caught in the area, according to monitoring tests conducted by TEPCO, the government and Fukushima Prefecture.

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